According to the National Academy of Sciences, the Earth's surface temperature has
risen by about 1 degree Fahrenheit in the past century, with accelerated warming during
the past two decades. There is new and stronger evidence that most of the warming over the
last 50 years is attributable to human activities. Human activities have altered the
chemical composition of the atmosphere through the buildup of greenhouse
gasesprimarily carbon dioxide, methane, and nitrous oxide. The heat-trapping
property of these gases is undisputed although uncertainties exist about exactly how
earth's climate responds to them.

A graph on this page shows global temperature variations for over a century

Figure 1

Larger warming changes, from about 2 to 10 degrees Fahrenheit, are predicted for the
present century. These projections are based on scientific models which, like all
scientific conclusions, are tentative, and they contain significant uncertainties. A view
of what there is a broad scientific consensus on and what is less well understood appears
on the linked EPA page

Scientists know for certain that human activities are changing the composition of
Earth's atmosphere. Increasing levels of greenhouse gases, like carbon dioxide (CO2 ), in
the atmosphere since pre-industrial times have been well documented. There is no doubt
this atmospheric buildup of carbon dioxide and other greenhouse gases is largely the
result of human activities.

. . .

Figuring out to what extent the human-induced accumulation of greenhouse gases since
pre-industrial times is responsible for the global warming trend is not easy. This is
because other factors, both natural and human, affect our planet's temperature. Scientific
understanding of these other factorsmost notably natural climatic variations,
changes in the sun's energy, and the cooling effects of pollutant aerosolsremains
incomplete.

. . .

The fundamental scientific uncertainties are these How much more warming will occur?
How fast will this warming occur? And what are the potential adverse and beneficial
effects?

A similar discussion of the global warming problem appears on the National
Oceanographic and Atmospheric Administration's site, "A Paleo Perspective on Global
Warming"

A number of alternative explanations of the observed climatic data have been put
forward. While the terrestrial land/water/atmosphere/heat system is extremely complex with
many only-partially-understood positive and negative feedback loops (e.g., the causes and
effects of cloud cover), there are only two major alternative explanations: volcanic
activity and variations in solar radiation.

In 1991, Mount Pinatubo put 8 cubic kilometers of ash in the atmosphere. The worldwide
temperature temporarily lowered 1 degree F from 1991 to 1993. The geologic record shows
that volcanoes that produce 1000 cubic kilometers of ash or greater happen about twice per
100,000 years on Earth. The last discovered was the volcano Toba in Sumatra. It erupted
about 76,000 years ago. Toba put 2800 cubic kilometers of ash in the atmosphere. In
theory, the worldwide temperatures in the temperate zones must have been below freezing
year around for several years in a row.

While volcanos can certainly have a large effect on climate, their effects are
transient. They produce large amounts of methane and carbon dioxide but massive volcanic
discharges are rare and their major effects last only for a few years, whereas
human-caused pollution is continuously renewed. There is no plausible volcanic explanation
for the observed warming trend of the last century.

Variations in solar irradience are a more serious alternative and will be given more
attention here.

The basic 22-year solar cycle (divided into two symmetrical northern/southern
hemisphere phases) is well understood

This article mentions cycles of 88 and 207 years and the 2300-year Halstatt cycle.

While some of the observed warming may be due to these cycles, they don't provide a
full explanation of the warming of recent decades. And, while there may be
still-longer-term cycles, they cannot explain the marked departure of global climate data
from expected values at the end of the twentieth century.

A sober dissent from the consensus on climate change appears in "Solar Activity A
Dominent Factor in Climate Dynamics," by Dr. Theodor Landscheidt of the Schroeter
Institute for Research in Cycles of Solar Activity, Nova Scotia, Canada

Dr. Landscheidt's paper refers to most of the cycles mentioned above and he makes some
very good points, but his data simply does not provide a viable alternative explanation
for the observed warming. On this page he provides a graph of satellite data on solar
intensity for the years 1979 to 1992

Figure 2

This obviously does not correspond to the warming data for this period shown in Figure
1.

It appears more possible that there could be a relationship in the following figure

Figure 3

The text accompanying the figure reads "The thick curve shows the Northern
Hemisphere surface temperature (right scale), while the thin line represents the length of
the 11-year sunspot cycle (left scale) covering the years 1865 to 1985."

When the figures are scaled properly, it appears that variations in solar radiation go
a long way toward explaining the observed warming, but the correlation breaks down for the
last two decades (not shown in Figure 3). Space-based measurements of solar irradience for
the last twenty years do not show the same sharp increase shown in the global temperature
data of Figure 1, as indicated in Figure 4 below, from "The Inconstant Sun"

Dr. Landscheidt wrote, "I forecasted, in 1982, that we should expect declining
temperatures after 1990 and probably a new Little Ice Age around 2030." This clearly
does not describe the real world of 1990-2003. Dr. Landscheidt is a serious scientist and
not a right-wing extremist with no significant scientific background, like many of those
whose anti-climate-science writings are to be found on the Internet and elsewhere, but
nothing in his 34-page article stands against the very real dangers posed by the unknowns
in this area, despite his erudition.

Like human beings, other living organisms are also very sensitive to variations in
temperature and precipitation. It is not necessary to understand precisely what variations
are brought about by human activity to see that agriculture and meat production are highly
dependent on climatic variations. Such variations can also bring about flooding or severe
water shortages with only a fairly small amount of change. Fresh water supplies are
already a big problem in many parts of the world. California is at the limit of the supply
needed for cities, wildlife, and agriculture, with no end to growth in sight.

I live in the mediterranean climate of the San Francisco Bay Area. Seasonal variations
are considerably less here than in many other areas. We don't have snow in the winter and
it rarely gets much above 100 degrees Fahrenheit on the hottest days, but the
relatively-mild extremes we do have are debilitating and my body performs suboptimally in
these conditions. In my lifetime, the weather around here has become significantly less
predictable (in the long term; short-term weather forecasting has gotten a lot better),
but one trend is clear the seasons start and end several weeks later than they did when I
was a child, half a century ago. Local climate is much more difficult to predict than
global climate on the basis of the models now available, but major changes have been
reported in many areas of the world and can be expected to be larger, with resulting
economic dislocation, if human industrial activity continues to increase.

The earth has warmed up by about one degree over the past century. Precipitation has
increased by one percent and sea levels have risen by 6 to 8 inches (source: the EPA
site). Human industrial activity, which is suspected as the likely cause, has greatly
increased. The models which are taken most seriously predict several degrees more of
warming and more changes in the water circulation cycle during the twenty-first century,
enough to raise sea levels significantly, alter natural ecosystems, and completely change
what kind of agriculture can be practiced where. Those who say this is not a problem have
their heads in the sand.

Unfortunately, many political conservatives have made opposition to climate science
part of their program and it's contributing to the widespread denial that there's a
problem. They need to take a long, hard look at their cousins who deny Darwinian evolution
to get an idea of how they're missing the boat on this issue. The Christian
fundamentalists have way too much influence in the Bush administration and their
willingness to ignore scientific facts when it suits them is terribly dangerous to sound
policy in this area. They have applied pressure to prevent the findings of environmental
agencies from influencing policy and have even suppressed data which did not support
administration policies, as has been widely reported in the news recently.

The "News Scan" (p. 20) in the August issue of Scientific American
contains a critique of a meta-analysis by Sallie Baliunas and Willie Soon of the Harvard
Smithsonian Center for Astrophysics which has attracted a great deal of attention
recently. Relying on a number of faulty assumptions, this study attempts to explain away
human effects on climate, and its emphasis on events prior to the twentieth century makes
it of questionable relevance in any case.

The following is from a website maintained by the "Cooler Heads Coalition," a
group of skeptics with regard to global warming

Projections of future climate changes are uncertain. Although some computer models
predict warming in the next century, these models are very limited. The effects of cloud
formations, precipitation, the role of the oceans, or the sun, are still not well known
and often inadequately represented in the climate modelsalthough all play a major
role in determining our climate. Scientists who work on these models are quick to point
out that they are far from perfect representations of reality, and are probably not
advanced enough for direct use in policy implementation. Interestingly, as the computer
climate models have become more sophisticated in recent years, the predicted increase in
temperature has been lowered.

We are, indeed, dealing with an extraordinarily complex system with many interdependent
factors. At the present state of the art, the models are fairly crudebut they're all
we've got. Weather forecasts aren't terribly accurate but we still rely on them in
planning activities. To a certain extent, the weather must be regarded as the luck of the
drawbut it still doesn't make sense to draw to an inside straight. Proceeding on the
assumption that human activity has a negligible effect on climate is no longer prudent.

Are humans causing the climate to change?
98% of total global greenhouse gas emissions are natural (mostly water vapor); only 2% are
from man-made sources.

That's all very well, but we're talking about a system in balance. Put 100
one-ounce weights on one side of a two-pan balance and 98 on the other and it's going to
tip.

Larger quantities of CO2 in the atmosphere and warmer climates would likely lead to an
increase in vegetation. During warm periods in history vegetation flourished, at one point
allowing the Vikings to farm in now frozen Greenland.

When the climate changes some places become warmer, others cooler, some wetter, others
drier. It's not just a question of how much vegetation there is but of the health of the
plants and animals we depend on for our food supply and the continued viability of crucial
ecosystems such as rainforests and marshes.

The ones who should be asking how accurate the models are are those who consider it
fine and dandy to charge forward with more human population growth, more economic
"development" and more destruction of our planet's fragile biosphere.

The policy questions raised by the skeptics are more serious. From the same page

Because of the devastating effects that global warming policies will have on economic
growth, the treaty that was discussed in Kyoto in December 1997 currently excludes
developing nations. However, the US Senate has voted 95-0 against supporting a treaty that
doesnt include developing nations.

As painful as it is, I have to agree with the Senate that exclusion of the
"developing" nations is a bad idea. "Developing" is the problem. If
the whole world "developed" to the same level of energy use as the United States
the problems discussed here would be multiplied disastrously. It's hard to see what real
advantage there is to humanity in uncontrolled growth, but the disadvantages are all too
obvious.

By all estimates, only severe reductions in global CO2 emissionson the order of
60 percent or morewill alter the computer forecasts. The resulting economic
dislocations would be tremendous, potentially outweighing the negative impacts of even the
most apocalyptic warming scenario.
If the policies do not include developing nations the result will likely be a reallocation
of emissions to developing nations, not a reduction of emissions.

Although cleaner technologies are possible, major reductions in emissions are at least
many decades away. There is only one practicable way to bring energy use and greenhouse
gas emission under control the world must get serious about population control. What is
needed is an actual reduction of the present world population. The earth can
sustainably support only about a billion people and there are over six billion of us at
present. (The figure I've chosen is my own subjective estimate; there's nothing special
about one billion, but the earth is clearly already overpopulated with humans and serious
study of what level of population is actually sustainable is needed.) Unfortunately, there
seems to be almost no interest even in preventing population increase at the
present time.

From an Associated Press story by Jim Abrams dated July 17, 2003:

On Tuesday the House voted 216-211 to sustain a policy under which recent Republican
presidents have withheld funds from the United Nations Population Fund.
Last year Bush denied the fund $34 million out of some $450 million the United States
contributed to international family-planning programs. Opponents of the fund say its
programs in China support forced abortions and sterilizations in that country.
"Since 1979, the UNFPA has been the chief apologist for China's coercive
one-child-per-couple policy," said Rep. Christopher Smith, R-NJ.

Prevention is better than forced abortions (and the Chinese often coerce women into
abortions even in the final month of pregnancy), but one-child-per-couple and
sterilization of those who've reached their reproductive quota or who have serious genetic
defects is the right way to go. Overpopulation is the heart of the problem and methods
rigorous enough to actually turn the growth trend around are urgently needed before
natural forces kill off billions of human beings; the carrying capacity of the earth is
finite, but few are willing to recognize this basic truth.

If the human race does not heed the warning signs there will be a collapse of
civilization as we know it, probably before the end of the present century. If this
happens, it will be much more difficult to reestablish our technology than it was to
create it in the first place. Some resources, like metals, can be harvested from dumps and
the wreckage of our present technology and reused; others, like petroleum, are
nonrenewable on the time scale of human civilization. And it's not only a matter of
depletion; there are also the discharge of poisons into the environment and massive
reductions in biodiversity to consider.

The main point, of course, is that, in the absence of definitive understanding of what
we're doing to our planet, it would be prudent for the human race to cool it for a while
and find out more about natural limits before proceeding with development-as-usual.

[A reference to an organization that I cannot now recommend has been
removed from the end of this essay.]